Palau’s Jellyfish Lake once had an outlet to the sea, but is now connected to the ocean through fissures and tunnels in the surrounding limestone. Millions of jellyfish were trapped in the basin when sea levels dropped, and over time they evolved into a species that have lost the ability to sting because they don’t have to fight off predators. Jellyfish Lake is a snorkeling and swimming extravaganza where you can get up close and personal with an estimated 10 million jellyfish.